Proving Grounds (Tank)

Hello, I'm looking for some advice regarding proving grounds.

Firstly I'm still deciding which class to use. The two classes I'm currently considering are warrior and death knight. I'm considerably more experienced tanking on my warrior than I am my death knight, although I'm not exactly a pro tank, I've spent the majority of my time dpsing on my warrior. Though, I prefer the proven defender title over all of them and it's something I'd like to get.

Along with that I'm not exactly sure which gear to use. I mean, I know the more sockets the better and I know that certain stats don't scale down very well but, I'm unsure of what I should be gemming in my sockets.

and I think the biggest question that I have is regarding trinkets. I currently don't have many tanking trinkets, although I do have the one from malkorak.

So basically,

1. Which class? Warrior or Death knight?
2. What should I be gemming in my sockets? (Is stamina or parry/dodge valued more?)
3. Which trinkets
4. General tips